Acne is a multifunctional disorder which commonly occurs during adolescence and which sometimes heals spontaneously but more often takes a long time and requires specific topical or systemic treatments with chemical substances such as benzoyl peroxide, retinoids, antibiotics and anti-androgens. Unfortunately some of these products can produce side-effects such as reddening, dryness of the skin and allergic reactions. Furthermore, one of the fundamental problems in treating acne and other skin diseases is crossing the epidermal layer, which represents the natural physiological barrier to the ingress of the drugs. Indeed to obtain a local pharmacological effect, topical application is used by administering the active principle formulated in ointments, creams or gels, used as vehicles.
Lecithin, a phospholipid of natural origin, is used in certain cosmetic or pharmaceutical preparations as the principal component or as an emulsifier. Its function, apart from being structural, can be functional in terms of carrying the active principle into the skin. Indeed the chemical similarity between lecithin (phosphatidyl choline) and the lipid components of the cell membranes suggests that vehicles based on lecithin can be well tolerated by the body and at the same time increase the pharmacological action (Scartazzini and Luisi, 1988 J. Physiol. Chem. 91, 823-833).
The term “acne” (from the Greek akni: efflorescence) describes the follicular lesions which appear during adolescence and which are linked with seborrhoea and the formation of comedones. It is an extremely common disease which, to a variable degree, affects approximately 90% of adolescents, but only 10% of these require medical intervention and only 1% of the latter pose clinical problems which are difficult to solve.
Acne is a chronic inflammation of the pilosebaceous apparatus which presents in various ways, as comedones, pustules, nodules, cysts and scars. There are many clinical varieties regarding appearance, course, age on onset and location. The most common form is juvenile acne which appears at puberty and resolves itself spontaneously around the age of 25, even though it can appear later, recur and regress after 30 years of age (Kraning et al. 1979 J. Invest. Dermatol. 73, 395-401).
Onset is generally during the age of development with typical skin lesions: comedones, papules, nodules and cysts. The comedones are follicles swollen with sebum, commonly called “whiteheads”, when the follicular orifice is closed and “blackheads” when the follicular orifice opens; they are distributed with greater frequency around the nose and on it, on the forehead, around and in the ears and finally on the chin. The papules are the inflammatory complication of the comedo and appear as reddened raised areas of various sizes. They last a few days and disappear without trace. Pustules are yellowish-coloured lesions, hemispherical in shape and pus-filled, which surmount the papules. They last two to three days and voided to the outside with scab formation. Nodules are large solid formations, often painful to pressure, produced by an inflammatory infiltrate. Cysts are large raised areas filled with pus, very painful to the touch, which remain unchanged for weeks and unlike the other acne lesions can easily turn into scars, these being the permanent consequences of acne which are unaesthetic and sometimes disfiguring.
The main pathogenic factors involved in the etiopathogenesis of acne are: 1) sebaceous hypersecretion; 2) follicular hyperkeratosis; 3) bacterial colonisation of the follicles; 4) the onset of an inflammatory process. Subjects with acne secrete more sebum than the controls and this factor seemed to be correlated with the severity of the acne. The development and secretory activity of the sebaceous glands is controlled by the androgenous hormones, produced by the testicle, by the ovary and by the adrenal glands.
Testosterone influences the proliferative activity of the sebaceous gland, which has receptors with a high affinity for these hormones and also has the enzyme 5-α-reductase, capable of converting testosterone into its biological active fraction, dihydrotestosterone. The hormonal factors are involved in the cyclical flare-ups of acne during the premenstrual phase in women.
Follicular hyperkeratosis is a fundamental event for the development of the acne lesions and is due in part to the increased proliferation of the epidermis and partly to the delayed detachment of the corneocytes. The result is a thickening of the follicular wall obstructing the exit of the sebum, which then stagnates and forms comedones. Under these conditions Propionibacterium Acnes, an anaerobic bacterium, tends to develop and to proliferate (Strauss et al., 1974 J. Invest. Dermatol. 62, 321-325; Harris et al., 1983 J. Am. Acad. Dermatol. 8, 200-203), producing free fatty acids with irritant and comedogenic capability stimulating the immune response. Finally, inflammation is due to the passage of biologically active substances from the pilosebaceous duct to the dermis. The treatments available can be divided into keratolytic and bacteriostatic treatments if they relate to cell reconstruction and antibacterial action respectively.
The therapeutic strategies depend on the severity of the disorder. Medicines for topical use are preferred for medium or moderate forms of acne. The most common creams are those based on benzoyl peroxide, which dries out the spots and blocks infection.
There are three kinds of topical treatment for acne available today. These are based on different mechanisms of action; retinoids, comedolytic agents, which slow down the process of desquamation in order to reduce the number of comedones and microcomedones; antibiotics, with bactericidal activity which act by directly killing the forms of P. acnes, also having a slight indirect effect on comedogenesis; combined therapy, using both retinoids and topical antibiotics, for patients who suffer from severe forms of acne, with comedonic and inflammatory lesions at the same time.
For not particularly serious acne phenomena Retin-A, also known as tretinoin, is an anticomedonic agent which is applied directly to the skin. Its action, in the form of a lotion or cream, is keratolytic, i.e. it restores the normal process of keratin formation and prevents the formation of comedones (blackheads).
Research in the dermatological field for new therapeutic solutions is constantly evolving. The latest generation of therapeutic solutions now available are the following:    1. Tazarotene, a synthetic product which interacts specifically with the receptors of vitamin A. As well as on acne, it is effective in the treatment of psoriasis;    2. Azelaic acid has produced alternative results in European studies and is characterised by a broad spectrum of dual action, both antimicrobial and keratinising; it is in fact also used in cases of cutaneous hyperpigmentation (Graupe et al., 1996, Cutis 57, 20-35); and    3. Adapalene, a derivative of naphthoic acid with retinoidal activity. This is a modulator of cell differentiation with a keratinising effect, which is effective and less irritating than retinoic acid. It is marketed under the name Differin® and is used for the topical treatment of acne vulgaris, where comedones, papules and pustules predominate.
The international patent application WO03/011808 describes a new class of compounds defined as atypical retinoid acids which are described as having anti-tumoral use. The compounds described in this application include adamantyl methoxydiphenyl propenoic acid (ST1898).